<script src="vue.js"></script>

<div id="app">
    <div v-bind:class="{box}">我是box
           <div v-bind:class="{inner}">我是inner1</div>
           <div v-bind:class="{inner}">我是inner2</div> 
    </div>
 </div> 

 <script> 
    var vue=new Vue({
           el:'#app',
           data:{ 
           box: 'box', 
           inner: 'inner' 
    }
    }); 
    </script> 
   
    <style> 
           .box {
      background-color: pink; 
      width:100%; 
      height:100%; 
           } 
    .inner{ 
      background-color: red; 
      width:80px; 
      height:100px; 
 } 
    </style>